Polyp Prevention 1996.
| Methods | RCT | |
| Participants | People with at least one adenomatous polyp of the large bowel removed (USA)
CVD risk: low Control: 1042 randomised, 943 analysed Intervention: 1037 randomised, 943 analysed Mean years in trial: control 3.05, intervention 3.05 % male: control 64%, intervention 66% Age: mean control 61.5, intervention 61.4 (all at least 35) Baseline BMI: mean control 27.5 (SE 0.12), intervention 27.6 (SE 0.13) |
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| Interventions | Low fat vs usual diet Control: general dietary guidelines Intervention: total fat 20%E, 18 g fibre/1000 kcal, 5 to 8 servings fruit and vegetables daily Control methods: leaflet, no additional information or behaviour modification Intervention methods: > 50 hours of counselling over 4 years, included skill building, behaviour modification, self monitoring and nutritional materials Weight goals: "weight loss is permitted but not encouraged....counselled to replace fat intake with increased intake of fruit, vegetable and grain products rather than reduce total calorie intake." Total fat intake (at 4 years): low fat 23.8 (SD 6.0), control 33.9 (SD 5.9) %E Saturated fat intake: unclear Style: diet advice Setting: community |
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| Outcomes | Stated trial outcomes: recurrence of polyps, prostate cancer Available outcomes: weight, total cholesterol |
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| Notes | Weight data reported at 1, 2, 3 and 4 years. 3‐year data used in main analysis. | |
| Risk of bias | ||
| Bias | Authors' judgement | Support for judgement |
| Random sequence generation (selection bias) | Low risk | "randomly assigned" by computer randomisation centre, stratified according to centre |
| Allocation concealment (selection bias) | Low risk | Phone call to computer randomisation centre, stratified according to centre |
| Blinding (performance bias and detection bias) All outcomes | High risk | Outcome assessors blinded, participants not |
| Incomplete outcome data (attrition bias) All outcomes | Low risk | 193 of 2079 (9%) lost over 3 years (< 5% per year) |
| Selective reporting (reporting bias) | Unclear risk | Protocol not seen |
| Other bias | Low risk | |
| Free of systematic difference in care? | High risk | 50 hours behaviour modification in intervention group, not in control. See 'Control methods' and 'Intervention methods' in the 'Interventions' section above |
| Free of dietary differences other than fat? | High risk | Fibre, fruit and vegetable goals in intervention group |